1. Technical Field
The present invention relates to data processing systems and, in particular, to remote method invocation in a Java environment. Still more particularly, the present invention provides a method, apparatus, and program for reusing remote method invocation connections.
2. Description of Related Art
Java is a programming language designed to generate applications that can run on all hardware platforms without modification. Java was modeled after C++, and Java programs can be called from within hypertext markup language (HTML) documents or launched stand alone. The source code of a Java program is compiled into an intermediate language called “bytecode,” which cannot run by itself. The bytecode must be converted (interpreted) into machine code at runtime. When running a Java application, a Java interpreter (Java Virtual Machine) is invoked. The Java Virtual Machine (JVM) translates the bytecode into machine code and runs it. As a result, Java programs are not dependent on any specific hardware and will run in any computer with the Java Virtual Machine software.
Remote Method Invocation (RMI) is a remote procedure call (RPC), which allows Java objects (software components) stored in a network to be run remotely. In the Java distributed object model, a remote object is one whose methods can be invoked from another JVM, on the same host or potentially on a different host.
Creating an RMI connection between two JVMs can be an expensive process both in terms of time and resources. Thus, it would be advantageous to reuse an established connection when possible. An RMI connection between two JVMs is encapsulated within a Java remote object. A connection can be reused by maintaining a normal reference to the connection object on the RMI client. In order to properly manage these connection objects, the RMI remote object class may implement the Unreferenced interface to allow the object to be notified when it is no longer referenced by a client JVM. When the object is notified via the Unreferenced interface, the object becomes unusable and can be destroyed in response to garbage collection by the server JVM. Garbage collection is a routine that searches memory for program segments or data that are no longer active in order to reclaim that space.
To prevent a remote object from becoming unreferenced and invoking the notification mechanism, a client JVM may hold a normal reference to the connection object. However, holding a normal reference to a connection object prevents the resources that it is using in the server JVM from being reclaimed until the client JVM releases the reference to the object. A problem may occur when the server JVM is instructed to shutdown. If a client JVM still holds a normal reference to a connection object connecting the client JVM to the server JVM, it can prevent or greatly delay the shutdown process of the server JVM. A problem may also occur if the server JVM is running low on memory resources. If the client JVM still holds a normal reference to a connection, the server JVM cannot reclaim the memory used for that object even though the connection may not be needed.
Thus, it would be advantageous to provide an improved mechanism for reusing established RMI connections.